The present invention relates to an inspecting apparatus designed for automatic sensor evaluation of a display screen such as a liquid crystal panel or the like.
While important researches and development have been made for liquid crystal panels in the past years, there is an inspection step in the manufacturing process of the liquid crystal panel to inspect the presence/absence of dust, foreign substance, irregularity or the like in the uniform background within the liquid crystal panel where the image density is changed. Although the inspection has been carried out through visual judgement with human eyes at present, its automatization is strongly required and therefore, enthusiastic attempts have been made to provide an automatic inspecting/evaluating apparatus for automatic evaluation of the display quality of the produced liquid crystal panel.
Particularly, when the sensor evaluation of the liquid crystal panel is to be automated, it has been performed by processing picture images through a TV camera or the like.
An example of a conventional display screen inspecting apparatus of the type referred to above will be described below with reference to FIGS. 4 and 5.
FIG. 4 is a structural diagram of the display screen inspecting apparatus. A liquid crystal panel 22 to be inspected is put on a positioning table 21 and illuminated by an illuminating device 23. A TV camera 24 for picking up an image of a display screen of the liquid crystal panel 22 is supported by a movable TV camera supporting body 25. The TV camera 24 is controlled by a TV camera control circuit 26.
An image signal input through the TV camera 24 is sent to an analog/digital conversion circuit (referred to as an A/D conversion circuit) 27, where the signal is digitized into image data of 0-255 gradations (256 gradations) in accordance with the density of the image. The digitized image data is input to a microcomputer including a CPU, a ROM, a RAM, an input/output port, and the like which constitute a fundamental part of the display screen inspecting apparatus.
The display screen inspecting apparatus includes a decision control circuit (CPU) 28 to which instructions are supplied from a main controller or an operating panel, an unacceptable portion enhancing circuit 29 which enhances an unacceptable portion to the background through the LUT (Lookup Table) conversion or the like of the input image, a binarization circuit 30 which converts the enhanced image into two digits, and a decision circuit 31 which makes a decision of the display screen on the basis of the size, etc. of the unacceptable portion separated from the background by the binarization circuit 30.
The inspecting apparatus of the above-described structure operates in a manner as follows.
As shown in a flow chart of FIG. 5, when the liquid crystal panel 22 is activated to inspect an unacceptable portion therein, the, display screen of the liquid crystal panel 22 is viewed by the TV camera 24 and the image of the display screen is input to the inspecting apparatus (step #11). The unacceptable portion enhancing circuit 29 processes the input image by Lookup Table conversion or image integration or the like, to thereby enhance the unacceptable portion (step #12). The binarization circuit 30 changes the enhanced image into two digits in order to separate the unacceptable portion from the background (step #13), and then the decision circuit 31 decides whether or not the display screen is acceptable based on the size or the like of the unacceptable portion (step #14).
In the arrangement as described hereinabove, however, it is difficult to enhance the unacceptable portion if it is low in contrast, for example, because of the irregular orientation or if it has modest change in the image density, since the decision is based only on the information from the state of the display screen driven by one driving voltage. Therefore, stable detection cannot be expected in the prior art.